In recent years the art of auto focussing cameras has developed to the point where a number of cameras that may automatically focus on an object are on the market. These systems may be divided into two categories, the first being the active system in which a beam of sound or light energy is transmitted from the camera to the object and the reflection is received by the camera and processed so as to determine the range to the object. The second category includes the passive systems in which light from the object is transmitted to the camera to produce two radiation patterns on two detector arrays spaced a known distance apart. The distance to the object is determined from the positions of the patterns on the two detector arrays.
One passive system has been proposed where light from the remote object passes through the taking lens of the camera and passes through a plurality of lenslets so as to create images of the exit pupil of the taking lens on pairs of detectors mounted behind the lenslets, the detectors usually being part of an integrated circuit chip. Such a system is found in my U.S. Pat. No. 4,185,191, issued Jan. 22, 1980.
One problem has been encountered in such systems due to the fact that the lenslets receiving light from the taking lens are molded in a transparent member which permits light not only to be focused by the lenslets on the detectors but also to be transmitted by the portions of the member which are adjacent the lenslets onto the integrated circuit chip. When this occurs, light striking the circuit areas in the chip may produce spurious signals that can produce error in the circuit operation. This appears to be caused by circuit elements which are light sensitive and produce unwanted carriers. Furthermore, when surface defects in the material adjacent the lenslets exist, scattering of light can be produced thus causing some light to reach the detector areas without passing through the lenslets which may also produce error in circuit operation.